1. Field of the Invention
This invention relates to magnetoresistive (MR) sensors and more particularly to MR sensor devices and methods of fabrication thereof.
2. Description of Related Art
U.S. Pat. No. 5,561,896 of Voegeli et al. for "Method of Fabricating Magnetoresistive Transducer" discloses a method referred to as a Selective Pulse Interdiffusion (SPI) process during which areas destined to become biasing segments of an MagnetoResistive (MR) head are selectively heated using one or more electrical current pulses of short duration. The transducer is a MR device with an H configuration wherein the cross bar of the H is the active central region of a soft magnetic layer. Short current pulses are passed through the side legs of the H to change the legs of the H into a hard magnetic material by annealing/resetting soft magnetic layers to cause interdiffusion between a soft magnetic layer (e.g. Permalloy) and an interdiffusion layer of Ti, Ta, Cr or possibly another transition or refractory metal.
U.S. Pat. No. 5,748,399 of Gill for "Resettable Symmetric Spin Valve" describes a method of annealing AFM layers using short current pulses passed through conductors to heat antiferromagnetic layers beyond their blocking temperatures.
U.S. Pat. No. 5,772,794 of Uno et al. for "Manufacturing Method of Magnetic Head/Apparatus with Spin Valve Effect Magnetoresistive Head" describes a stack of two thin film layers of soft ferromagnetic material separated a thin film layer of a nonmagnetic material, with one of the first and second thin film layers being pinned by a thin film AFM layer. The stack is annealed after the layers are formed to form a uniaxial anisotropy in the pinned soft magnetic layer.
U.S. Pat. No. 5,859,753 of Ohtsuka et al. for "Spin Valve Magneto-resistive Head With Spun Valves Connected in Series" shows a Spin Valve MR head that sets AFM layers that have different blocking temperatures using only two annealing steps. The head includes two magnetization pinning layers, anti-parallel to each other, including AFM layers one of which is NiMn that has a high blocking temperature and one of which is FeMn that has a low blocking temperature. At col. 10, lines 10-19". . . NiMn having a high blocking temperature is formed as the first antiferro-magnetic layer . . . on the first magnetization pinning layer . . . at a temperature of 200.degree. to 300.degree. C. The NiMn is grown in a magnetic field H.sub.01 applied in the first direction. Thereafter, . . . FeMn is formed as the second antiferromagnetic layer . . . on the second magnetization spinning layer . . . at a temperature of around 160.degree. C. While applying a magnetic field H.sub.02 in the direction opposite to the first direction, the growth of FeMn is carried out." At Col. 10, lines 37-60 it is pointed out that an alternative process can employ a step of heating to the higher blocking temperature and application of field H.sub.01 which is followed by a step of heating to the lesser blocking temperature temperature and application of magnetic field H.sub.02 can be deferred until after formation of the AFM layers.
U.S. Pat. No. 5,856,897 of Mauri for "Self-Biased Dual Spin Valve Sensor" shows a Dual Spin Valve (DSV) MR sensor with a free magnetic layer between two pinned magnetic layers.